Selective β-glucuronidase inhibitors as a treatment for side effects of camptothecin antineoplastic agents

ABSTRACT

Compounds, compositions and methods are provided that comprise selective β-glucuronidase inhibitors for both aerobic and anaerobic bacteria, especially enteric bacteria normally associated with the gastrointestinal tract. The compounds, compositions and methods can be for inhibiting bacterial β-glucuronidase and for improving efficacy of camptothecin-derived antineoplastic agents or glucuronidase-substrate agents or compounds by attenuating the side effects caused by reactivation by bacterial β-glucuronidases of glucuronidated metabolites of camptothecin-derived antineoplasatic agents or glucuronidase-substrate agents or compounds.

This application is a continuation of U.S. Ser. No. 13/514,418, filedAug. 27, 2012, which is the U.S. National Stage of InternationalApplication No. PCT/US2010/059690, filed Dec. 9, 2010, which designatesthe U.S. and was published by the International Bureau in English onJun. 16, 2011, and which claims the benefit of U.S. Provisional PatentApplication No. 61/285,265, filed Dec. 10, 2009, and 61/408,032, filedOct. 29, 2010; the contents of each of which are hereby incorporatedherein in their entirety by reference.

GOVERNMENT SUPPORT

This invention was made with government support under Grant NumberCA098468 awarded by the National Institutes of Health. The governmenthas certain rights in the invention.

FIELD OF THE INVENTION

The invention relates generally to compositions and methods forinhibiting enteric bacterial enzymes and for attenuating side effects ofantineoplastic agents, and more particularly to compositions and methodsfor inhibiting bacterial β-glucuronidases and for attenuating sideeffects of camptothecin-derived antineoplastic agents orglucuronidase-substrate agents or compounds used in the treatment ofvarious neoplasms or other conditions.

BACKGROUND

Camptothecin, a plant alkaloid derived from the Chinese Camptothecaacuminata tree, was added to the National Cancer Institute's naturalproducts screening set in 1966. It showed not only strong antineoplasticactivity, but also poor bioavailability and toxic side effects. Afterthirty years of modifying the camptothecin scaffold, two camptothecinderivatives emerged and are now approved for clinical use. The firstderivative is topotecan (also called Hycamptin®; GlaxoSmithKline;London, England), which can be used to treat solid brain, lung andovarian tumors. The second derivative is irinotecan (also called CPT-11and Camptosar®; Pfizer; New York City, N.Y.), which can be used to treatsolid brain, colon and lung tumors, as well as refractory forms ofleukemia and lymphoma.

The sole target of camptothecin and camptothecin-derived antineoplasticagents is human topoisomerase I. Camptothecin and camptothecin-derivedantineoplastic agents bind to covalent topoisomerase I-DNA complexes andprevent re-ligation of broken single DNA strands, effectively trappingit on the DNA. Such immobilized macromolecular adducts act as roadblocksto the progression of DNA replication and transcription complexes,causing double-strand DNA breaks and apoptosis. Structural studies haveestablished that camptothecin and other camptothecin-derivedantineoplastic agents stack into duplex DNA, replacing the base pairadjacent to the covalent phosphotyrosine linkage. See, Chrencik et al.(2004) J. Mol. Biol. 339:773-784; and Staker et al (2002) Proc. Natl.Acad. Set. USA 99:15387-15392. Re-ligation of the nicked DNA strand isprevented by increasing the distance between the 5′-hydroxyl and the3′-phosphotyrosine linkage to >11 Å. Because neoplastic cells growrapidly, camptothecin and other camptothecin-derived antineoplasticagents impact these cells more significantly than normal cells andtissues.

Camptothecin-derived antineoplastic agent efficacy, including that ofcamptothecin, is limited by a delayed diarrhea that follows itsadministration by about two to four days. For example, “reactivation” ofSN-38G, a glucuronidated inactive metabolite of irinotecan, to SN-38,its active metabolite, by β-glucuronidases of enteric bacteria killsintestinal epithelial cells and causes a dose-limiting diarrhea. See,e.g., Matsui et al. (2003) Surg. Oncol. Clin. N. Am. 12:795-811; andTobin et al. (2003) Oncol. Rep. 10:1977-1979.

While broad-spectrum antibiotics have been used to eliminate entericbacteria from the gastrointestinal tract prior to irinotecan treatmentto reduce reactivation, this approach has several drawbacks. First,enteric bacteria (i.e., normal flora) play essential roles incarbohydrate metabolism, vitamin production and the processing of bileacids, sterols and xenobiotics. Thus, a partial or complete removal ofenteric bacteria is not ideal for subjects already challenged byneoplastic growths and chemotherapy. Second, the elimination of thesymbiotic enteric bacteria from even healthy subjects significantlyincreases risk of infection by pathogenic bacteria, includingenterohemorrhagic Escherichia coli and Clostridium difficile. Third,bacterial antibiotic resistance is a human health crisis, and theunnecessary use of antibiotics is a significant contributor to thiscrisis.

Likewise, weak/non-selective β-glucuronidase inhibitors such assaccharic acid 1,4-lactone can be administered to reduce reactivation.These inhibitors, however, are only partially effective in preventingreactivation of glucuronidated metabolites of camptothecin and othercamptothecin-derived antineoplastic agents. Fittkau et al. (2004) J.Cancer Res. Clin. Oncol. 130:388-394. Additional non-specific inhibitorsof β-glucuronidase include certain divalent cations (e.g., Cu²⁺ andZn²⁺), galacturonic acid and glucuronic acid. Naleway, “Histochemical,spectrophotometric, and fluorometric GUS substrates” 61-76 In: GUSProtocols: Using the GUS Gene as a Reporter of Gene Expression(Gallagher ed., Academic Press 1992); and Handbook of Enzyme Inhibitors,Part A (Zollner ed., 2^(nd) ed. 1993).

For the foregoing reasons, there is a need for alternative compositionsand methods for inhibiting bacterial β-glucuronidases and forattenuating reactivation of glucuronidated metabolites of camptothecinand other camptothecin-derived antineoplastic agents or any otherglucuronidase-substrate agents or compounds.

BRIEF SUMMARY

Compositions and methods are provided for selectively inhibitingbacterial β-glucuronidases. Accordingly, compositions of the presentinvention include β-glucuronidase inhibiting agents that selectivelyinhibit bacterial β-glucuronidases from hydrolyzing glucuronides. Theselectively inhibiting agents can be provided as formulated compositionsand can be administered to subjects in need thereof. In particular, theselectively inhibiting agents or compositions comprising such agents canbe administered prior to, concurrently with or after an antineoplasticagent, particularly a camptothecin-derived antineoplastic agent, totreat a variety of neoplasms including cancers, or in the same mannercan be used with any other glucuronidase-substrate agent(s) orcompound(s). When used together, the selectively inhibiting agentreduces side effects of antineoplastic agents or any otherglucuronidase-substrate agent(s) or compound(s), thus improving efficacyof the antineoplastic agent or other agents.

The selectively inhibiting agents and compositions can be used inmethods for treating cancer and for reducing side effects ofantineoplastic agents, such as camptothecin-derived antineoplasticagents. Thus, the gastrointestinal distress that typically accompaniestreatment with an antineoplastic agent can be attenuated. The methodsare also useful for attenuating or improving any adverse reactionsassociated with administration of glucuronidase-substrate agent(s) orcompound(s).

Methods of the present invention include administering to a subject inneed thereof a therapeutically effective amount of at least oneβ-glucuronidase inhibiting agent that selectively inhibits bacterialβ-glucuronidases from hydrolyzing glucuronides.

The present invention provides the first potent, selective inhibitors ofbacterial β-glucuronidases in both aerobic and anaerobic bacteriaassociated with the gastrointestinal tract.

The following embodiments are encompassed by the present invention.

1. A compound having selective β-glucuronidase inhibitor activity, thecompound selected from the group consisting of:

and active derivatives thereof.

2. A composition comprising at least one compound selected from thegroup consisting of the compounds of embodiment 1.

3. The composition of embodiment 2 further comprising a pharmaceuticallyacceptable carrier.

4. The composition of embodiment 2 or 3 wherein said composition isadministered prior to, concurrently with, or after the administration ofat least one camptothecin-derived antineoplastic agent 5. Thecomposition of embodiment 4, wherein at least one camptothecin-derivedantineoplastic agent is selected from the group consisting ofcamptothecin, diflomotecan, exatecan, gimatecan, irinotecan,karenitecin, lurtotecan, rubitecan, silatecan and topotecan.

6. The composition of any of embodiments 2-5, wherein the at least oneselective β-glucuronidase inhibitor is at a concentration from about 1nM to about 1 mM.

7. A method for selectively inhibiting bacterial β-glucuronidases, themethod comprising administering to a subject in need thereof aneffective amount of at least one selective β-glucuronidase inhibitor.

8. The method of embodiment 7, wherein the at least one selectiveβ-glucuronidase inhibitor is selected from the compounds of embodiment1.

9. The method of embodiment 8, wherein the at least one selectiveβ-glucuronidase inhibitor is administered to the subject at aconcentration from about 1 nM to about 1 mM.

10. The method of embodiment 7, wherein the bacterial β-glucuronidasesare enteric bacterial β-glucuronidases.

11. The method of embodiment 10, wherein the bacteria are selected fromthe group consisting of a Bacteroides sp., Bifidobacterium sp.,Catenabacterium sp., Clostridium sp., Corynebacterium sp., Enterococcusfaecalis, Enterobacteriaceae, Lactobacillus sp., Peptostreptococcus sp.,Propionibacterium sp., Proteus sp., Mycobacterium sp., Pseudomonas sp.,Staphylococcus sp. and Streptococcus sp.

12. A method for improving camptothecin-derived antineoplastic agentefficiency, the method comprising administering to a subject prior to,concurrently with or after administration of a camptothecin-derivedantineoplastic agent a therapeutically effective amount of at least oneselective β-glucuronidase inhibitor.

13. A method for attenuating side effects in a subject beingadministered a camptothecin-derived antineoplastic agent, the methodcomprising administering prior to, concurrently with or afteradministration of a camptothecin-derived antineoplastic agent atherapeutically effective amount of at least one selective3-glucuronidase inhibitor.

14. The method of embodiment 12 or 13, wherein the at least oneselective β-glucuronidase inhibitor is selected from the compounds ofembodiment 1.

15. The method of embodiment 12 or 13, wherein the camptothecin-derivedantineoplastic agent is selected from the group consisting ofcamptothecin, diflomotecan, exatecan, gimatecan, irinotecan,karenitecin, lurtotecan, rubitecan, silatecan and topotecan.

16. The method of embodiment 15, wherein the camptothecin-derivedantineoplastic agent is irinotecan.

17. A method to alleviate gastrointestinal distress associated withchemotherapy comprising:

-   -   a) administering to an animal an anti-cancer effective amount of        a chemotherapeutic agent, and    -   b) administering to the same animal an inhibitory effective        amount of a β-glucuronidase inhibitor.

18. The method of embodiment 17, wherein the chemotherapeutic activeagent is a camptothecin-derived antineoplastic agent.

19. The method of embodiment 17, wherein the 3-glucuronidase inhibitoris selected from the group consisting of:

and active derivatives thereof.

20. A method for improving the efficiency of a glucuronidase-substrateagent or compound, the method comprising administering to a subjectprior to, concurrently with or after administration of said agent orcompound a therapeutically effective amount of at least one selectiveβ-glucuronidase inhibitor.

21. The method of embodiment 20, wherein said selective β-glucuronidaseinhibitor is selected from the group consisting of:

and active derivatives thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood and features, aspectsand advantages other than those set forth above will become apparentwhen consideration is given to the following detailed descriptionthereof. Such detailed description makes reference to the followingdrawings, wherein:

FIG. 1A shows a diagram of the activation and metabolism of irinotecan.FIG. 1B shows the structure of irinotecan, as well as its active (SN-38)and inactive (SN-38G) metabolites.

FIG. 2A shows a three-dimensional image of an E. coli β-glucuronidasedimer and tetramer. FIG. 2B shows a crystallographic image of an E. coliβ-glucuronidase tetramer in its active form.

FIG. 3A shows an illustration of a native crystal structure of E. coli3-glucuronidase in which the active site is occluded by a loop (topimage), and an image of a glucaro-δ-lactam (GDL)-bound E. coliβ-glucuronidase in which the loop shifted (bottom image). FIG. 3B showsa graphic representation of the loop shifting at the active site.

FIG. 4A shows a structure of each of the nine selective β-glucuronidaseinhibitors described herein. FIG. 4B shows a graph depicting a reductionin absorbance that represents decreasing β-glucuronidase with anincrease in β-glucuronidase inhibitor concentration (inhibitor 9) of E.coli β-glucuronidase (left bar at each concentration) compared to bovineβ-glucuronidase (right bar at each concentration) (abscissa is inhibitorconcentration in mM; ordinate is relative absorbance). FIG. 4C shows agraph depicting a significant effect of the selective β-glucuronidaseinhibitors on β-glucuronidase activity of E. coli under anaerobic (leftbar at each treatment) and aerobic (right bar at each treatment)conditions (abscissa is treatment condition; ordinate is relativeabsorbance). FIG. 4D shows a graph depicting efficacy of the selectiveβ-glucuronidase inhibitors on the obligate anaerobe Bacteroides vulgatus(abscissa is treatment condition; ordinate is relative absorbance).

FIG. 5 shows a superimposed image of E. coli β-glucuronidase and Homosapiens β-glucuronidase.

FIG. 6 shows an alignment of primary β-glucuronidase sequences from E.coli (see SEQ ID NO: 1) and H. sapiens (see SEQ ID NO: 2).

FIG. 7 shows an illustration of residues of interest for the interactionof GDL with the active site of β-glucuronidase.

FIG. 8 shows a modeling of the shift in the active site ofβ-glucuronidase.

FIG. 9 shows illustrations of various substrates for β-glucuronidaseassays.

FIG. 10 shows a graph depicting a reduction in absorbance of mutant E.coli lacking β-glucuronidase or a mutant E. coli having a vectorencoding for β-glucuronidase compared to wild-type E. coli (left bar is0 mM IPTG; right bar is 0.3 mM IPTG) (abscissa is E. coli cell type;ordinate is relative absorbance).

FIG. 11 shows a graph depicting a relatively weak effect of GDL in vitro(left bar is in vitro treatment; right bar is in vivo treatment)(abscissa is GDL concentration (mM); ordinate is relative absorbance).

FIG. 12 shows a graph depicting a lack of significant effect of theselective β-glucuronidase inhibitors on viability/cell survival of E.coli (abscissa is treatment condition; ordinate is colony formingunits).

FIG. 13 shows a graph depicting a lack of cytotoxicity of the selectiveβ-glucuronidase inhibitors on human colonic cells (abscissa is treatmentcondition; ordinate is relative fluorescence signal).

FIG. 14A shows illustration of an E. coli β-glucuronidase in which theactive site is bound to SN-38G. FIG. 14B shows a structuralrepresentation of FIG. 14A. FIG. 14C shows an illustration an E. coliβ-glucuronidase in which the active site is bound to inhibitor 9. FIG.14D shows a structural representation of FIG. 14C.

While the present invention is susceptible to various modifications andalternative forms, exemplary embodiments thereof are shown by way ofexample in the drawings and are herein described in detail. It should beunderstood, however, that the description of exemplary embodiments isnot intended to limit the invention to the particular forms disclosed,but on the contrary, the intention is to cover all modifications,equivalents and alternatives falling within the spirit and scope of theinvention as defined by the appended claims.

DETAILED DESCRIPTION

Overview

The present invention relates to an identification of potent (i.e., lowuM to high pM), selective β-glucuronidase inhibitors for both aerobicand anaerobic bacteria, especially those bacteria associated with thegastrointestinal tract (i.e., enteric bacteria). The present inventiontherefore includes compositions and methods for inhibiting bacterialβ-glucuronidases and for improving efficacy of camptothecin-derivedantineoplastic agents or glucuronidase-substrate agents or compounds byattenuating the gastrointestinal distress caused by reactivation ofglucuronidated metabolites of such agents.

Compounds of interest herein include:

and active derivatives thereof.

As used herein, “active derivative” and the like means a modifiedβ-glucuronidase inhibiting compound that retains an ability toselectively inhibit bacterial β-glucuronidases. For example, thederivative can be capable of inhibiting β-glucuronidase reactivation ofSN-38G to SN-38, but not killing bacteria that inhabit thegastrointestinal tract or inhibiting mammalian β-glucuronidases. One ofskill in the art is familiar with assays for testing the ability of anactive derivative compound for selectively inhibiting β-glucuronidaseswith no toxicity to the bacteria that inhabit the gastrointestinaltract. See, Experimental section below.

As used herein, “inhibit,” “inhibiting” and the like means thatβ-glucuronidase expression, activity or function and thereforemetabolite reactivation can be reduced in a subject. Likewise,“attenuate” means to reduce or lessen. That is, the 3-glucuronidaseactivity can be reduced. Likewise, the side effects of achemotherapeutic agent can be reduced. Thus, to inhibit or attenuatemeans a reduction of at least about 5%, about 10%, about 15%, about 20%,about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 85%,about 90%, about 95% or up to about 100% as compared to an appropriatecontrol.

As used herein, “selectively inhibit” and the like means that aβ-glucuronidase inhibitor reduces bacterial, but not mammalian,β-glucuronidase activity. That is, the β-glucuronidase inhibitor canbind to and can prevent bacterial, but not mammalian, β-glucuronidasesfrom hydrolyzing glucuronides.

As used herein, “β-glucuronidase” and the like means an enzyme (EC3.2.1.31) capable of hydrolyzing β-glucuronides, but not β-glucuronidesor β-glucosides. See, Basinska & Florianczyk (2003) Ann. Univ. MariaeCurie Sklodowska Med. 58:386-389; Miles et al. (1955) J. Biol. Chem.217:921-930. As used herein, a “glucuronide” and the like means asubstance produced by linking glucuronic acid to another substance via aglycosidic bond. Examples of glucuronides of interest herein include,but are not limited to, glucuronides of camptothecin-derivedantineoplastic agents such as SN-38G (7-ethyl-10-hydroxycamptothecinglucuronide).

As used herein, “camptothecin-derived antineoplastic agent” and the likemeans a cytotoxic quinoline alkaloid that inhibits the DNA enzymetopoisomerase I. A camptothecin-derived antineoplastic agent can includea structure comprising at least the following:

Camptothecin-derived antineoplastic agents include, but are not limitedto, camptothecin (i.e.,(S)-4-ethyl-4-hydroxy-1H-pyrano[3′,4′6,7]indolizino[1,2-b]quinoline-3,14-(4H,12H)-dione);diflomotecan (i.e.,(5R)-5-ethyl-9,10-difluoro-1,4,5,13-tetrahydro-5-hydroxy-3H,15H-oxepino[3′,′:6,7]indolizino[1,2-b]quinoline-3,15-dione);exatecan (i.e.,(1S,9S)-1-amino-9-ethyl-5-fluoro-1,2,3,9,12,15-hexahydro-9-hydroxy-4-methyl-10H,13H-benzo(de)pyrano(3′,4′:6,7)indolizino(1,2-b)quinoline-10,13-dione);gimatecan (i.e.,(4S)-11-((E)-((1,1-dimethylethoxy)imino)methyl)-4-ethyl-4-hydroxy-1,12-dihydro-14H-pyrano(3′,4′,6,7)indolizino(1,2-b)quinoline-3,14(4H)-dione);irinotecan (i.e.,(S)-4,11-diethyl-3,4,12,14-tetrahydro-4-hydroxy-3,14-dioxo1H-pyrano[3′,4′:6,7]-indolizino[1,2-b]quinolin-9-yl-[1,4′bipiperidine]-1′-carboxylate);karenitecin (i.e.,(4S)-4-ethyl-4-hydroxy-11-(2-trimethylsilyl)ethyl)-1H-pyrano[3′,4′:6,7]indolizino[1,2-b]quinoline-3,14(4H,12H)-dione);lurtotecan (i.e.,7-(4-methylpiperazinomethylene)-10,11-ethylenedioxy-20(S)-camptothecin);rubitecan (i.e.,(4S)-4-ethyl-4-hydroxy-10-nitro-1H-pyrano[3,4′:6,7]indolizino[1,2-b]quinoline-3,14(4H,12H)-dione);silatecan (i.e., 7-tert-butyldimethylsilyl-10-hydroxycamptothecin); andtopotecan (i.e.,(S)-10-[(dimethylamino)methyl]-4-ethyl-4,9-dihydroxy-1H-pyrano[3′,4′:6,7]indolizino[1,2-b]quinoline-3,14(4H,12H)-dione).

Of interest herein is irinotecan (CPT-11 or Camptosan®), which is apotent camptothecin-derived antineoplastic agent for treating solidmalignancies of the brain, colon and lung, as well as refractory formsof leukemia and lymphoma. Irinotecan is a prodrug that must be convertedinto its active form, SN-38 (7-ethyl-10-hydroxycamptothecin), to haveantineoplastic activity. During its excretion, SN-38 is glucuronidatedto SN-38 glucuronide (SN-380) by phase II drug metabolizingUDP-glucuronosyltranserases.

The term “glucuronidase-substrate agent(s) or compound(s)” refers to anydrug, agent or compound or, in particular, a metabolite thereof that canbe a substrate for glucuronidase. Thus, in some instances, a drug,compound or agent that is not itself a substrate, but is metabolized toa substrate is encompassed by the term as used herein. Any drug,compound or agent or metabolite thereof that is glucuronidated, alsoreferred to as glucuronides, can be a substrate for glucuronidase and isalso described herein as glucuronidase-substrate agent(s) orcompound(s). Many drugs, agents or compounds undergo glucuronidation atsome point in their metabolism. Alternatively, the drug, agent orcompound may be a glucuronide pro-drug. These glucuronides may havedifferent properties than the parent drug, agent or compound.Glucuronidation can modulate the potency of some drugs: the6-glucuronide of morphine is a more potent analgesic than the parentcompound, whereas the 3-glucuronide is a morphine antagonist. Inaddition, steroid glucuronidation can produce more active or toxicmetabolites under pathophysiological conditions or during steroidtherapies.

Drugs, agents or compounds or metabolites thereof which are substratesfor glucuronidase can have their respective properties altered byglucuronidase hydrolysis. In a specific, non-limiting example, if thedrug, agent, compound or metabolite thereof has been metabolized to aglucuronide, the hydrolysis of the glucuronide can reactivate the drug,agent, compound or metabolite thereof. In many cases, this reactivationcan cause adverse reactions. For example, if a glucuronide drug, agentor compound or metabolite thereof is present in the gut, glucuronidasehydrolysis in the gut can lead to gastrointestinal distress.

The methods described herein are useful for attenuating, ameliorating orimproving the adverse reactions, such as gastrointestinal distress,caused by the action of glucuronidase on a drug, agent or compound or,in particular, a metabolite thereof. As described fully elsewhereherein, hydrolysis of glucuronides can lead to adverse reactions. Themethods described herein inhibit or decrease the activity ofβ-glucuronidases. The methods can therefore be useful to attenuate,ameliorate or improve adverse reactions, such as gastrointestinaldistress, associated with administering such drugs, agents or compounds.The methods can also improve the tolerance of any such drug, agent orcompound or metabolite thereof that can form a glucuronide. As such,administration of a glucuronidase inhibitor can rescue or improve atreatment with any drug, agent or compound, wherein glucuronidasehydrolysis of a glucuronide related to the drug, agent, compound ormetabolite thereof is causing one or more adverse reactions,particularly gastrointestinal distress or toxicity. Patient complianceand outlook would also improve with the lessening of adverse reactions.

Reactivation of inactive metabolites such as SN-38G to active SN-38occurs in the gastrointestinal tract and results from bacterialβ-glucuronidases. As noted above, the reactivated metabolites can leadto a gastrointestinal distress such as diarrhea, which often can be adose-limiting side effect of the cancer therapy or the therapy to treatany other conditions. As used herein, “dose-limiting” indicates that theside effect from administration of a camptothecin-derived antineoplasticagent or glucuronidase-substrate agents or compounds prevents a subjectin need of cancer therapy or therapy to treat any other conditions fromreceiving a recommended amount. As increasing amounts of thecamptothecin-derived antineoplastic agent or glucuronidase-substrateagents or compounds are administered to a subject, increased amounts ofglucuronidated metabolites are therefore available as a substrate forthe bacterial β-glucuronidases. The resulting reactivated metabolitesnot only adversely affect a subject's well-being by causing serious sideeffects, particularly gastrointestinal distress, but also impairtreatment outcome by limiting the amount of the camptothecin-derivedantineoplastic agent or glucuronidase-substrate agents or compounds thatcan be administered to the subject.

The selective β-glucuronidase inhibiting compounds, compositions, andmethods of use thereof described herein are useful in a variety ofapplications. For example, the compounds, compositions and methodsdisclosed herein can be used for discovering additional selectiveβ-glucuronidase inhibitors in a screening assay as controls in whichpotential selective β-glucuronidase inhibitors can be compared.

The selective β-glucuronidase inhibiting compounds, compositions andmethods of use thereof also can be used to improve efficacy ofcamptothecin-derived antineoplastic agents or glucuronidase-substrateagents or compounds by attenuating the side effects associated withtheir administration during the treatment of various neoplasms or otherconditions. As used herein, “neoplasm” and the like means an abnormalgrowth of cells or a mass of tissue resulting from an abnormalproliferation of cells. Neoplasms frequently result in a lump or tumorand can be benign, pre-malignant (i.e., pre-cancerous) or malignant(i.e., cancerous growths including primary or metastatic cancerousgrowths). “Neoplastic” means of or related to a neoplasm. Thus, theselective β-glucuronidase inhibiting compounds and compositions can beused to improve treatment of a variety of neoplasms including, but notlimited to, neoplasms of the bone, brain, breast, cervix, colon,intestines, kidney, liver, lung, pancreatic, prostate, rectum, stomach,throat, uterus, and the like. The term “conditions” refers to anydisease or disorder for which the glucuronidase-substrate agents orcompounds are being primarily administered.

Compositions

The present invention provides compounds and compositions forselectively inhibiting bacterial β-glucuronidases. The compounds andcompositions can include an effective amount of at least one selectiveβ-glucuronidase inhibitor selected from the inhibitors described herein.As used herein, “effective amount” and the like means that amount of aninhibitor or other therapeutic agent that will elicit a biological ormedical response of a cell, tissue, system or animal that is beingsought, for instance, by a researcher or clinician. That is, theeffective amount of a selective β-glucuronidase inhibitor or compositionthereof is an amount sufficient to reduce or attenuate side effects ofcamptothecin-derived antineoplastic agents or glucuronidase-substrateagents or compounds. Particularly, the effective amount is that amountof the selective β-glucuronidase inhibitor or composition thereof toattenuate the side effects in a subjected being treated with acamptothecin-derived antineoplastic agent or glucuronidase-substrateagents or compounds. More particularly, the effective amount is thatamount sufficient to inhibit reactivation of glucuronidated metabolitessuch as SN-38G to SN-38. For example, the effective amount of theselective β-glucuronidase inhibitor can be about 1 pM to about 1 mM,about 1 nM to about 1 mM, about 1 M to about 1 mM, about 1 mM to about 1nM, about 1 nM to about 1 μM, or about 1 μM to about 1 mM.

As used herein, “about” means within a statistically meaningful range ofa value such as a stated concentration range, time frame, molecularweight, volume, temperature or pH. Such a range can be within an orderof magnitude, typically within 20%, more typically still within 10%, andeven more typically within 5% of a given value or range. The allowablevariation encompassed by “about” will depend upon the particular systemunder study, and can be readily appreciated by one of skill in the art.

Examples of selective β-glucuronidase inhibitors include, but are notlimited to,

and active derivatives thereof.

Advantageously, the β-glucuronidase inhibitors described herein areselective for bacterial β-glucuronidases. That is, the compounds inhibitβ-glucuronidase in bacteria but do not have inhibitory activity towardmammalian β-glucuronidases, including human β-glucuronidase. While notintending to be bound by any particular mechanism of action, thecompounds appear to bind a ˜12 residue loop in bacterialβ-glucuronidases that hovers over an active site opening. The loop isnot present in mammalian β-glucuronidases, which therefore canaccommodate larger substrates and cleave glucuronic acid moieties fromlong-chain glycosaminoglycans.

The β-glucuronidase inhibitors exhibit other advantages. For example,the compounds do not kill the enteric bacteria or harm human epithelialcells, but are effective against bacteria cultured under aerobic andanaerobic conditions.

The present invention also provides compositions comprising theselective β-glucuronidase inhibitors. The compositions can include atleast one selective β-glucuronidase inhibitor selected from theinhibitors described herein and a pharmaceutically acceptable carrier.The compositions are formulated to administer an effective amount to asubject in need thereof.

As used herein, “pharmaceutically acceptable” or “pharmacologicallyacceptable” means a material that is not biologically, physiologicallyor otherwise undesirable to a subject, i.e., the material may beadministered to the subject in a formulation or composition withoutcausing any undesirable biological effects or interacting in adeleterious manner with any of the components of the composition inwhich it is contained.

The pharmaceutically acceptable carrier can be a solid or liquid and thetype can be generally chosen based on the type of administration beingused. The selective β-glucuronidase inhibitor can be administered in theform of a tablet or capsule, as an agglomerated powder or in a liquidform. Examples of solid carriers include, but are not limited to,lactose, sucrose, gelatin and agar. Capsule or tablets can be easilyformulated and can be made easy to swallow or chew; other solid formsinclude granules, and bulk powders. Tablets can contain suitablebinders, lubricants, diluents, disintegrating agents, coloring agents,flavoring agents, flow-inducing agents, and melting agents.

Examples of liquid dosage forms include solutions or suspensions inwater, pharmaceutically acceptable fats or oils, alcohols or otherorganic solvents, including esters, emulsion, elixirs, syrups, solutionsand/or suspensions reconstituted from non-effervescent granules andeffervescent preparations reconstituted from effervescent granules. Suchliquid dosage forms can contain, e.g., suitable solvents, preservatives,emulsifying agents, suspending agents, diluents, sweeteners, thickenersand melting agents. Oral dosage forms can contain flavorants andcoloring agents.

The compositions of the invention also can include minerals and/orvitamins such as, calcium, vitamin A, vitamin B, vitamin D and vitaminE.

Methods

The present invention provides methods for selectively inhibitingbacterial β-glucuronidases. In the methods, an effective amount of atleast one selective β-glucuronidase inhibitor can be administered to asubject in need thereof. That is, a subject being treated with acamptothecin-derived antineoplastic agent or glucuronidase-substrateagents or compounds.

As used herein, “enteric bacteria” and the like mean the normal bacteriathat inhabit the human gastrointestinal track. Examples of entericbacteria include, but are not limited to, Bacteroides sp. (e.g.,Bateroides vulgatus), Bifidobacterium sp. (e.g., Bifidobacterium bifidumand Bifidobacterium infantis), Catenabacterium sp., Clostridium sp.,Corynebacterium sp., Enterococcus sp. (e.g., Enterococcus faecalis),Enterobacteriaceae (e.g., Escherichia coli), Lactobacillus sp.,Peptostreptococcus sp., Propionibacterium sp., Proteus sp.,Mycobacterium sp., Pseudomonas sp. (e.g., Pseudomonas aeruginosa),Staphylococcus sp. (e.g., Staphylococcus epidermidis and Staphylococcusaureus) and Streptococcus sp. (e.g., Streptococcus mitts). Becauseenteric bacteria commensally inhabit the gastrointestinal tract, theypromote gastrointestinal health by preventing infection by opportunisticbacteria like Clostridum difficle.

Methods for assessing β-glucuronidase activity are known in the art.See, e.g., Farnleitner et al. (2002) Water Res. 36:975-981; Fior et al.(2009) Plant Sci. 176:130-135; and Szasz (1967) Clin. Chem. 13:752-759.β-glucuronidase activity of bacteria provided the selectiveβ-glucuronidase inhibitor can be reduced by at least about 5%, 10%, 15%,20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%,90%, 95%, 96%, 97%, 98%, 99% or 100% when compared to bacteria notprovided the selective β-glucuronidase inhibitor.

The present invention also provides methods for improving efficacy ofcamptothecin-derived antineoplastic agents or glucuronidase-substrateagents or compounds by attenuating reactivation by bacterialβ-glucuronidases of glucuronidated metabolites of camptothecin-derivedantineoplastic agents or glucuronidase-substrate agents or compounds. Inthe methods, a therapeutically effective amount of at least oneselective β-glucuronidase inhibitor can be administered to a subjecthaving or about to have treatment with a chemotherapeutic agent,particularly a camptothecin-derived antineoplastic agent or any otherglucuronidase-substrate agents or compounds.

As used herein, “subject” means a mammal including but not limited to acat, dog, horse, mouse, rat, non-human primate and human, but preferablya human.

The therapeutically effective amount of the at least one selectiveβ-glucuronidase inhibitor can be administered to the subject prior to,concurrently with or after administration of a camptothecin-derivedantineoplastic agent or glucuronidase-substrate agent or compound. Whenthe selective β-glucuronidase inhibitor is administered prior to thecamptothecin-derived antineoplastic agent or glucuronidase-substrateagent or compound, it can be as a prophylactic measure. For example, theselective β-glucuronidase inhibitor can be provided about 2 weeks, 1week, 6 days, 5 days, 4 days, 3 days, 2 days, 1 day, 12 hours, 10 hours,8 hours, 6 hours, 5 hours, 4 hours, 3 hours, 2 hours, 1 hour or even 30minutes prior to or after the camptothecin-derived antineoplastic agentor glucuronidase-substrate agent or compound.

The compounds and compositions are generally administered via an oralroute. However, any route of administration that will provide thecompounds to the intestine can be used.

One of skill in the art understands that the effective amount providedto a subject in need thereof can and will vary depending upon severalclinical parameters. For example, the therapeutically effective amountof the selective β-glucuronidase inhibitor will depend on the subjectbeing treated (e.g., age, weight, sex, etc.), the severity of thedisorder or disease, and the route of administration. Likewise, thetherapeutically effective amount will vary depending upon clinical andtreatment parameters.

In an embodiment, the subject matter described herein is directed to theuse of a selective β-glucuronidase inhibitor for the manufacture of amedicament for the use in selectively inhibiting bacterialβ-glucuronidases, for improving camptothecin-derived antineoplasticagent efficiency, for attenuating side effects in a subject beingadministered a camptothecin-derived antineoplastic agent, foralleviating gastrointestinal distress associated with chemotherapy, andfor improving the efficiency of a glucuronidase-substrate agent orcompound.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of skill in the artto which the invention pertains. Although any methods and materialssimilar to or equivalent to those described herein can be used in thepractice or testing of the present invention, the preferred methods andmaterials are described herein.

The following examples are offered by way of illustration and not by wayof limitation.

EXPERIMENTAL

Camptothecin, a plant alkaloid derived from the Chinese Camptothecaacuminata tree, was added to the NCI natural products screening set in1966. It showed strong antineoplastic activity but poor bioavailabilityand toxic side effects. After thirty years of modifying the camptothecinscaffold, two derivatives emerged and are now approved for clinical use.(Pizzolato & Saltz (2003). Lancet 361:2235-2242). Topotecan (Hycamptin®;GlaxoSmithKline) is currently employed to treat solid ovarian, lung andbrain tumors. Id. CPT-11 (also called Irinotecan, and Camptosar®;Pfizer) contains a carbamate-linked dipiperidino moiety thatsignificantly increases bioavailability in mammals. Id. Thisdipiperidino group is removed from the CPT-11 prodrug in vivo bycarboxylesterase enzymes that hydrolyze the carbamate linkage to producethe drug's active metabolite, SN-38. (Smith et al. (2006) Toxicol InVitro 20:163-175). CPT-11 is currently used to treat solid colon, lungand brain tumors, along with refractory forms of leukemia and lymphoma.(Pommier (2006) Nat Rev Cancer 6:789-802).

The sole target of the camptothecins is human topoisomerase I. (Hsianget al. (1985) J Biol Chem 260:14873-14878). This enzyme relievessuperhelical tension throughout the genome and is essential for DNAmetabolism, including DNA replication, transcription and homologousrecombination. (Redinbo et al. (1999) Curr Opin Struct Biol 9:29-36).Topoisomerase I breaks one strand in duplex DNA, forming a covalent3′-phosphotyrosine linkage, and guides the relaxation of DNA supercoils.(Redinbo et al. (1998) Science 279:1504-1513; Stewart et al. (1998)Science 279:1534-1541). It then reseals the single-strand DNA break andreleases a relaxed duplex DNA molecule. The camptothecins bind to thecovalent topoisomerase I-DNA complex and prevent the religation of thebroken single DNA strand, effectively trapping the 91 kDa protein on theDNA. (Hsiang, 1985). Such immobilized macromolecular adducts act asroadblocks to the progression of DNA replication and transcriptioncomplexes, causing double-strand DNA breaks and apoptosis. (Pommier,2006). Because cancer cells are growing rapidly, the camptothecinsimpact neoplastic cells more significantly than normal human tissues.Structural studies have established that the camptothecins stack intothe duplex DNA, replacing the base pair adjacent to the covalentphosphotyrosine linkage. (Chrencik et al. (2004) J Mol Biol 339:773-784;Staker et al. (2002) Proc Natl Acad Sci USA 99:15387-15392). Religationof the nicked DNA strand is prevented by increasing the distance betweenthe 5′-hydroxyl and the 3′-phosphotyrosine linkage to >11 Å. Id.

CPT-11 efficacy is severely limited by delayed diarrhea that accompaniestreatment. (Mathijssen et al. (2001). Clin. Cancer Res 7:2182-2194).While an early cholinergic syndrome that generates diarrhea within hourscan be successfully treated with atropine, the diarrhea that appears˜2-4 days later is significantly more debilitating and difficult tocontrol. (Ma & McLeod (2003) Curr Med Chem 10:41-49). CPT-11 undergoes acomplex cycle of activation and metabolism that directly contributes todrug-induced diarrhea (FIG. 1A). Id. CPT-11 administered by intravenousinjection can traffic throughout the body, but concentrates in the liverwhere it is activated to SN-38 by the human liver carboxylesterase hCE1(FIG. 1B). The SN-38 generated in the liver is eliminated from the bodyvia glucuronidation to SN-38G by the phase II drug metabolizingUDP-glucuronosyltransferase (UGT) enzymes (FIG. 1B). (Nagar & Blanchard(2006) Drug Metab Rev 38:393-409). SN-38G is excreted from the liver viathe bile duct and into the GI. Once in the intestines, however, SN-38Gserves as a substrate for bacterial β-glucuronidase enzymes in theintestinal flora that remove the glucuronide moiety and produce theactive SN-38 (FIGS. 1A-B). (Tobin et al. (2003) Oncol Rep 10:1977-1979).SN-38 in the intestinal lumen produced in this manner contributes toepithelial cell death and the severe diarrhea that limits CPT-11efficacy. This effect has been partially reversed in rats using therelatively weak (IC₅₀=90 μM) β-glucuronidase inhibitor saccharic acid1,4-lactone. (Fittkau et al. (2004) J Cancer Res Clin Oncol130:388-394).

While broad-spectrum antibiotics have been used to eliminate entericbacteria from the gastrointestinal tract prior to CPT-11 treatment(Flieger et al. (2007) Oncology 72:10-16), this approach has severaldrawbacks. First, intestinal flora play essential roles in carbohydratemetabolism, vitamin production, and the processing of bile acids,sterols and xenobiotics. (Cummings & Macfarlane (1997) JPEN J ParenterEnteral Nutr 21:357-365; Guarner & Malagelada (2003) Lancet361:512-519). Thus, the partial or complete removal of enteric bacteriais non-ideal for patients already challenged by neoplastic growths andchemotherapy. Second, it is well established that the elimination of thesymbiotic GI flora from even healthy patients significantly increasesthe chances of infections by pathogenic bacteria, includingenterohemorrhagic E. coli and C. difficile. (Job & Jacobs (1997) DrugSaf 17:37-46; Levy & Marshall (2004) Nat Med 10:S122-129; Nord et al.(1984) Am J Med 76:99-106; Settle & Wilcox (1996) Aliment Pharmacol Ther10:835-841; Sears et al. (1999) Gastrointest Endosc 50:841-844; Stamp(2004) Med Hypotheses 63:555-556; Yang & Pei (2006) World JGastroenterol 12:6741-6746). Third, bacterial antibiotic resistance is ahuman health crisis, and the unnecessary use of antimicrobials is asignificant contributor to this problem. (Levy & Marshall, 2004).

β-glucuronidases hydrolyze glucuronic acid sugar moieties in a varietyof compounds. (Basinska & Florianczyk (2003) Ann Univ Mariae CurieSklodowska Med 58:386-389). The presence of β-glucuronidases in a rangeof bacteria is exploited in commonly-used water purity tests, in whichthe conversion of 4-methylumbelliferyl glucuronide (4-MUG) to4-methylumbelliferone (4-MU) by β-glucuronidases is assayed to detectbacterial contamination. (Farnleitner et al. (2002) Water Res.36:975-981). While the crystal structure of human β-glucuronidase wasreported in 1996 (Jain et al. (1996) Nat Struct Biol 3:375-381), nostructure of a bacterial β-glucuronidase has been presented. Inaddition, whereas relatively weak inhibitors of β-glucuronidase havebeen reported (K_(i) values of 25 μM to 2 mM) (Russell & Klaenhammer(2001) Appl Environ Microbiol 67:1253-1261), no potent and/or selectiveinhibitors of the bacterial enzymes have been presented.

Results:

E. coli β-Glucuronidase Crystal Structure:

To understand bacterial β-glucuronidase activity and inhibition, weover-expressed, purified and crystallized full-length E. coliβ-glucuronidase in both the apo and inhibitor-bound state forexamination through x-ray diffraction. Native data were collected to 2.5Å resolution and data for crystals containing inhibitor-bound enzymewere collected to 2.4 Å resolution; however, initial attempts atmolecular replacement using the previously solved human β-glucuronidasemodel (PDB: 1 bhg, (Jain et al. (1996) Nat Struct Mol Biol 3:375-381))were unsuccessful. As such, selenomethionine substituted E. coliβ-glucuronidase was expressed, purified and crystallized to acquirenecessary experimental phases to solve the bacterial structure.Selenomethionine crystal data were collected to 2.9 Å, and experimentalphases were acquired using the SAD method. These phases were used tobuild the initial model. Molecular replacement using the SeMet model wasutilized on both the native and inhibitor-bound structure. Datacollection and final refinement statistics are shown in Table 1.

TABLE 1 Data Collection and Refinement Statistics. Data Collection X-raySource APS SER-CAT BM-22 Space group C2 Unit cell: a, b, c, (Å); α, β, γ(°) 168.9, 77.3, 126.6; 90, 125.0, 90 Data set SeMet Native GDL-boundWavelength (Å) 0.97926 1.0000 1.0000 Resolution (Å) 50.00-2.90 50.0-2.50 50.0-2.40 highest shell (3.00-2.90) (2.59-2.50) (2.49-2.40)I/σ 22.9 (3.7)  21.9 (2.4)  35.2 (4.1)  Completeness (%) 99.2 (93.7)96.5 (82.4) 98.6 (93.9) Redundancy 7.4 (6.3) 5.2 (3.3) 7.0 (6.2) Phasingand Refinement Resolution (Å)  50-2.9  50-2.5  50-2.4 No. reflections26483 43507 50982 Mean figure of merit 0.74 R_(work) 0.253 0.214 0.203R_(free) 0.282 0.267 0.254 Molecules per asymmetric unit 2 2 2 (AU) No.of free amino acids per AU 1192 1194 1194 No. of waters per AU 214 358355 Average B-factors 48.8 60.5 55.1 R.M.S. deviations Bond lengths (Å)0.016 0.003 0.010 Bond angles (°) 2.223 0.815 1.580 Ramachandran (%)Preferred 96.7 97.0 98.4 Allowed 2.7 2.4 1.3 Outliers 0.6 0.6 0.3

The asymmetric unit in both the native and inhibitor-bound structurescontains two monomers, each composed of 597 ordered residues (FIG. 2A).Two residues at the C-terminus of the enzyme, K602 and Q603, lackedelectron density, as did a disordered loop region from 363-369; as such,these regions were not placed in the final model. The N-terminal domainof E. coli β-glucuronidase (residues 1-180) contains 12 β-strands andtwo short α-helices, which resembles the sugar binding domain of thesecond family of glycosyl hydrolases³⁰. The C-terminal domain (274-603)forms an αβ-barrel (Jacobson et al. (1994) Nature 369:761-766) composedof 8 short β-strands and 9 α-helices, and contains the active siteresidues E413 and E504. Between the N- and C-terminal domain (181-273)exists an immunoglobin-like β-sandwich domain consistent with otherfamily 2 glycosyl hydrolases containing 7 β-strands. Id. The threedomains of the protein were assigned using BLAST. (Marchler-Bauer et al.(2009) Nucleic Acids Res 37:13205-210). Crystallographic symmetrygenerates the tetramer (FIG. 2B) expected to be the active form of theenzyme as calculated by gel filtration (data not shown).

Superimposing the E. coli β-glucuronidase structure with the structureof the human enzyme reveals 1.4 Å r.m.s.d. over 565 equivalent Cαpositions (FIG. 5). The E. coli structure contains one loop of ˜12-17residues in length not found in the human structure. Furthermore, thehuman structure contains structural elements not seen in the bacterialstructure, including two loops approximately 9-11 residues longer thanthe equivalent E. coli loop, and two short helices, which areunstructured loops in the bacterial structure. In spite of thesedifferences, the active sites of the bacterial and human enzymes alignwell, although in the unliganded E. coli structure a 7-8 residue loop isdisordered in the absence of the inhibitor (see below). Other majordifferences between the human and E. coli structures can be seen insolvent-exposed regions, such as loop residues that shift by 5.6-12.4 Åbetween the two proteins. An alignment of the primary β-glucuronidasesequence from E. coli and Homo sapiens reveal a 45% identity relative tothe E. coli sequence (FIG. 6). In addition, only one residue within 5 Åof the putative catalytic residues is not conserved between the twosequences.

The 2.4 Å resolution glucaro-δ-lactam (GDL)-bound structure reveals asingle clear binding mode of the inhibitor within the β-glucuronidaseactive site (FIG. 2B). GDL forms direct contacts with four amino acids(D163, R562, K568, Y472, H330) and one of the catalytic residues (E413),and is located 2.8 Å from the second catalytic residue, E504 (FIG. 7).The inhibitor-bound structure shares 1.2 Å r.m.s.d. over 597 equivalentCα atoms when superimposed on the 2.5 Å resolution structure of thenative, unliganded enzyme. The most significant site of difference(shifts in backbone position ≧2.8 Å) between the two structures occursat the active site (FIG. 3A-B). The entrance to the active site in thenative structure is occluded by the 466-476 loop that contains tyrosines468, 469 and 472, such that this loop would clash sterically with theobserved position of the GDL inhibitor (FIG. 3A). In the inhibitor-boundstructure, this loop has shifted in position to relocate these aromaticresidues 7-14 Å away and allow the GDL molecule to bind (FIGS. 3A-B).Upon this shift, the open area of the active site presents itself on thesurface of the molecule, which results in a shift from 10.9 Å²(unliganded) to 20.8 Å² (inhibitor-bound) (see FIG. 8), and Y472 forms adirect contact with the GDL molecule (FIG. 7). Thus, a conformationalchange is involved in inhibitor binding to the E. coli β-glucuronidaseactive site.

Inhibitors Identification through High-Throughput Screening:

To discover novel inhibitors of E. coli β-glucuronidase, high-throughputscreening was conducted using a 35,000-compound chemical library. A wellestablished β-glucuronidase assay was also employed, in which theconversion of 4-methylumbelliferyl-glucuronide (4-MUG) to4-methylumbelliferone (4-MU) is monitored by measuring the increase in4-MU fluorescence (excitation at 365 nm, emission at 450 nm) (FIG. 9).This assay is widely employed to test water samples for bacterialcontamination. (Farnleitner, 2002). It exhibited robust characteristics,with a screening Z-score of 0.84. (Zhang et al. (1999) J Biomol Screen4:67-73). The hit rate was 0.3% for the 100 compounds that produced 90%inhibition or better, exhibited good Hill coefficients and R² values forinhibition curves of 0.99 or better. Nine compounds representative ofthe chemical diversity of the hits were chosen for further investigation(FIG. 4A). It was noted, however, in considering the chemical structuresof these hits that the potential for absorbance or fluorescence waspossible and may interfere with subsequent characterization in vitro orin cells. For example, compounds 1-4,6,7 and 9 were found to absorb at˜355 nm, close to the excitation wavelength of the 4-MUG assay (data notshown).

Thus, two other β-glucuronidase activity assays were employed to examinethe potency of inhibitors both in vitro and in cell-based studies. Anabsorbance assay based on the conversion of p-nitrophenyl glucuronide(PNPG) to p-nitrophenol (PNP) (Szasz (1967) Clin Chem 13:752-759), whichabsorbs at 410 nm, was employed as the primary in vitro assay (FIG. 9).A secondary assay involving the conversion of phenolphthaleinglucuronide (PheG) to phenolphthalein (Phe), which absorbs at 540 nm,was also employed (FIG. 9). Id. Both assays were validated in vitro andin living cells, and the wavelengths monitored did not overlap withabsorbance characteristics of putative inhibitors (data not shown).Importantly, as outlined below, these assays recapitulated the in vitrohigh-throughput screening results obtained with the 4-MUG substrate.Control experiments were also performed to show that the enzyme activitydetected in cell-based assays was dependent on the presence of expressedβ-glucuronidase. For example, E. coli cells lacking a β-glucuronidasegene showed no enzyme activity using PNPG as a substrate; but when abacterial β-glucuronidase was expressed in those and wild-type cellslines, enzyme activity increased accordingly (FIG. 10). Theglucaro-δ-lactam (GDL) inhibitor examined in the crystal structure of E.coli β-glucuronidase exhibited relatively in vitro weak IC50 values of45±3.1 μM using PNPG and was ineffective in cells (FIG. 11).

Potent Inhibition In Vitro and in Living Aerobic and Anaerobic BacterialCells:

The nine representative compounds chosen from the high-throughputscreening results (FIG. 4A) were all more potent than glucaro-δ-lactamin vitro, and eight of the nine were effective in living cells as well(Table 2). FIG. 4B shows a typical graph of the reduction in absorbancerepresenting decreasing β-glucuronidase activity with an increase ofinhibitor concentration. In vitro, six (1, 2, 4, 5, 8 and 9) of the nineinhibitors had nanomolar-level IC₅₀ values, and the other three (3, 6and 7) had values of less than 2 μM. Compound 9 proved to be thestrongest inhibitor with an IC₅₀ value of 1.17±0.50 nM (Table 2).Cell-based assays in living E. coli cells were also conducted on each ofthe nine compounds; EC₅₀ values are presented Table 2. The potency ofinhibition improved in cells relative to in vitro for compounds 1, 2, 4,5, and 7; however, compounds 6 and 8 showed no improvement, and compound3 was ineffective. The efficacy of compound 9 remained strong in cells,with an EC₅₀ value of 3.58±1.80 nM. To assess the validity of theseresults, cell survival was tested in the presence of 100 μM of each ofthe nine inhibitors, as well as 1 mM of the hydrolysis products, PNP andPhe. The nine compounds exhibited no significant effect on cell survival(FIG. 12). Thus, potent inhibition of β-glucuronidase activity wasachieved in E. coli cells growing in aerobic conditions.

TABLE 2 Effect of the Inhibitor Compounds in Two β-Glucuronidase Assays.Inhib- PNPG PheG itor IC₅₀ (nM) EC₅₀ (nM) IC₅₀ (nM) EC₅₀ (nM) 1  282.5 ±26.05 17.7 ± 7.42 277.3 ± 30.4 29.0 ± 3.33 2 585.7 ± 31.1  233.2 ± 2.99600.8 ± 55.3 221.2 ± 22.01 3  1624 ± 1.32 1688.9 ± 24.12 4 369.3 ± 2.5128.3 ± 2.11  377.8 ± 13.71 33.2 ± 8.18 5 230.6 ± 1.17 92.4 ± 1.34 212.6± 17.9 99.9 ± 23.0 6 1058.2 ± 3.54  1322.8 ± 1.15  1067.2 ± 33.2  1302.5± 15.7  7 1204.6 ± 1.70   811 ± 1.35 1266.4 ± 86.12 913.3 ± 20.4  8740.1 ± 20.4 776.9 ± 6.44  721.7 ± 31.3 793.1 ± 27.9  9  1.17 ± 0.503.58 ± 1.80 0.984 ± 0.37 3.41 ± 1.13

Because over 99% of the bacterial species present GI tract are obligateanaerobes (Sears (2005) Anaerobe 11:247-251), E. coli cells grown underanaerobic conditions were tested, as well as other relevant anaerobicbacterial species. (Hawksworth et al. (1971) J Med Microbiol 4:451-459).The cell-based assay using anaerobic E. coli yielded similar results tothose of the aerobic conditions (FIG. 4C). Furthermore, in-cell assaysusing the obligate anaerobe Bacteroides vulgatus also demonstratedinhibitor efficacy (FIG. 4D), L. reuteri and B. infantis were alsotested, which do not contain the β-glucuronidase gene, (Russell &Klaenhammer, 2001; Grill et al. (1995) Curr Microbiol 31; 23-27) andfound no evidence of enzyme activity or inhibitor impact on assay signal(data not shown). As such, these cell lines are effective negativecontrols. Taken together with the in vitro and cell-based data outlinedabove, these results confirm that we have identified several novelpotent inhibitors of β-glucuronidase activity that are effective inliving aerobic and anaerobic bacterial cells lines but do not impactmicrobial cell survival.

With the identification of novel inhibitors of β-glucuronidase activity,the next step was taken to further characterize the compounds' effectson human intestinal cells, similar to those likely to be encountered inthe colonic region of the gastrointestinal tract. HCT116 (Brattain etal. (1981) Cancer Res 41:1751-1756), human colonic epithelial cells weretreated with each of the nine inhibitors to test the viability of thesecells to grow in their presence. Using the CellQuanti-Blue“ ” Assay Kit,the HCT116 cells were treated with the inhibitors, and checked for humancytotoxicity; the results show that the potent inhibitors do not effecthuman colonic cells (FIG. 13). The specificity of the nine compounds wastested by exploring their effects on a mammalian β-glucuronidase. Invitro assays were conducted using bovine liver β-glucuronidase in asimilar manner to that of the bacterial enzyme assay. With a range of 0to 100 μM inhibitor concentration of each of the nine inhibitors, it wasobserved that they have little to no effect on the activity of thismammalian β-glucuronidase (FIG. 4B).

Discussion:

The first crystal structure of a bacterial β-glucuronidase enzyme isreported herein, as well as structures of both the unliganded proteinand complexed with an inhibitor. A significant shift in the position ofan active site loop upon ligand binding reveals that conformationalchange may be involved in the formation of all substrate and inhibitorcomplexes with the enzyme (e.g., FIG. 3B). The residues on this loop(466-474 and 503-505) are nearly fully conserved between the bacterialand human β-glucuronidases; thus, a similar “induced fit” mechanism maybe at play in eukaryotic β-glucuronidases as well. Importantly,knowledge of the changes in structure that can occur at the bacterialβ-glucuronidase active site can be employed in the in silica screeningand validation of additional potential enzyme inhibitors. In addition,the binding of SN-38G (see FIG. 1) and compound 9 (see FIG. 4A) into theβ-glucuronidase active site (FIGS. 14A-B) were modeled. Several criticalinteractions are formed between conserved catalytic gorge residues onthe enzyme (e.g., Y468, Y472, N466, and D163) and functional groups onthe substrate and inhibitor. Additionally, both compounds take on acurved shaped, allowing them to fit tightly into the curved tunnel ofthe active site. These models provide a useful place to begin to developimproved inhibitors by structure-based design.

The nine compounds that were characterize further from the 300 plus hitsfrom high-throughput screening all are effective inhibitors of theβ-glucuronidase enzyme in vitro (with IC₅₀s of 1 nM-1.6 μM), and eightof the nine maintain 3 nM-1.3 μM efficacy in living bacterial cells.Furthermore, they exhibit β-glucuronidase inhibition in anaerobicconditions and against an obligate anaerobe, Bacteroides vulgatus, knownto be a significant component of the human gastrointestinal microflora.(Sears, 2005). Importantly, however, the inhibitors characterized heredo not impact bacterial cell growth or survival. This was a desiredcharacteristic of compounds designed to be used in conjunction withCPT-11. Effective β-glucuronidase inhibitors would reduce SN-38reactivation in the GI without eliminating these commensal bacteria thatpromote health and prevent infection by opportunistic bacteria likeClostridium difficile. (Guarner & Malagelada 2003; Job & Jacobs, 1997).

In medicinal applications, these potent inhibitors can contact the humanepithelial cell lining in the intestine. HCT116 human colonic epithelialcells were incubated with the nine compounds in order to test them forcytotoxic effects on mammalian cells. As shown (FIG. 13), the inhibitorshave little to no cytotoxicity, and these cells continue to be viable intheir presence. As such, novel potent inhibitors have been discoveredthat not only inhibit β-glucuronidase in vivo, but are also non-toxic tobacterial cells lines, anaerobic and aerobic, as well as humanepithelial cells known to inhabit the GI tract. This is a crucialstarting point to move into more clinical settings.

To assess the selectivity of the nine compounds a mammalianβ-glucuronidase, from bovine liver, was incubated and tested for enzymeactivity in their presence. The nine compounds appear to not inhibitthis mammalian enzyme as they do the bacterial (data not shown, see FIG.4B for example). These results suggest that the inhibitors show a fairamount of selectivity towards the bacterial enzyme. Preliminary analysisvia sequence and structural alignment (see FIGS. 5-6) indicates that the˜12 residue loop (362-374) in the E. coli β-glucuronidase that hoversover the active site opening, of which is missing in the human enzyme(bovine liver β-glucuronidase is 82% identical and is also missing thisloop region), may play a part in this issue. The major role of themammalian version of the enzyme is to cleave the glucuronic acid moietyfrom long chain glycosaminoglycans. (Ray et al. (1999) J Hered90:119-123; Eudes et al. (2008) Plant Cell Physiol 49:1331-1341). Assuch, these enzymes must have the ability to accommodate these largesubstrates. The lack of this loop region would allow for a more openactive site and avenue for larger substrates to reside. This loopregion, which is present in the bacterial enzyme, would suggest thatsmall molecules, such as glucuronide linked xenobiotics (Eudes, 2008)would have a tighter fit in the active site such that the enzyme wouldbe turned “off” more frequently.

CPT-11 is currently used largely in combination with a number ofwell-known chemotherapeutics (Masuda et al. J Clin Oncol 10:1775-1780;Saltz et al. (1996) Eur J Cancer 32A Suppl 3:S24-31) but can still beemployed as a single agent in colorectal cancer. (Armand et al. (1995)Eur J Cancer 31A:1283-1287; Shimada et al. (1996) Eur J Cancer 32A Suppl3:Sβ-17). To improve the outcome for subject on CPT-11 alone, andpotentially to allow more single agent use, one can reduce the diarrheathat limits dose intensification and efficacy. An approach can be toinhibit the β-glucuronidase enzyme known to reactivate SN-38G to SN-38in the lower gastrointestinal tract. Such inhibitors are potent andeffective in living bacterial cells, but do not kill the bacteria thatinhabit the gastrointestinal tract.

Materials and Methods:

Expression and Purification of E. coli β-Glucuronidase.

The full-length E. coli β-glucuronidase gene was obtained from genomicDNA and was cloned into the pET-28a expression plasmid (Novagen) with anN-terminal 6×-Histidine tag. BL2′-DE3 competent cells were transformedwith the expression plasmid and grown in the presence of kanamycin (25ug/ml) in LB medium with vigorous shaking at 37° C. The expression wasinduced with the addition of 0.3 mM IPTG and further incubated for 4hours. Cells were centrifuged at 4500×g for 20 min at 4° C. forcollection. Cell pellets were resuspended in Buffer A, along with PMSFand protease inhibitors containing aprotinin and leupeptin. Resuspendedcells were lysed by sonication and clarified by centrifugation. Proteinwas purified by Ni-chromatography column followed by gel filtration.

Selenomethionine Substituted β-Glucuronidase.

B834 competent cells were transformed with pET-28a containing theβ-glucuronidase gene. SelenoMet™ Medium and Nutrient Mix (AthenaES) wereprepared for growth, with 50 mg of selenomethionine added for each literof medium. The cells were grown and induced the same as the nativeβ-glucuronidase. The temperature was lowered to 15° C. and the culturesgrown overnight with shaking.

Crystallization, Data Collection, and Phasing.

Crystals were obtained at 2 mg/mL protein in 15% PEG3350, 0.2 MMagnesium Acetate, and 0.02% Sodium Azide at 16° C. Crystals werecryo-protected with perfluoropolyether oil (Sigma) and flash cooled inliquid nitrogen. Diffraction data were collected on the 22-BM beam lineat SER-CAT (Advanced Photon Source, Argonne National Laboratory). Datawere indexed and scaled using HKL2000. (Otwinowski et al., “Processingof X-ray diffraction data collected in oscillation mode” 307-326 In:Methods in Enzymology, Vol. 276 (Academic Press 1997)). Selenomethioninedata were collected to 2.9 Å and processed similarly. The PHENIXsoftware suite was utilized to locate heavy atom sites and to trace aportion of the model. (Adams et al. (2002) Acta Crystallogr D BiolCrystallogr 58:1948-1954). An initial model was built in Coot using theSAD data and used with Phaser for molecular replacement. (Emsley &Cowtan (2004) Acta Crystallogr D Biol Crystallogr 60:2126-2132; McCoy etal. (2007) J Appl Crystallogr 40:658-674). The structure was refinedusing simulated annealing and torsion angle refinement in CNS, andmonitored using both the crystallographic R and cross-validating R-freestatistics. (Brunger (1997) Methods Enzymol 277:366-396). Datacollection and refinement statistics are presented in Table, 1. PHENIXwas used for anisotropic B-factor and TLS refinement. (Adams, 2002). Themodel was manually adjusted using Coot and 2F_(o)-F_(c) and F_(o)-F_(c)electron density maps. The GDL model and definition files were generatedusing PRODRG. (Schuttelkopf & van Aalten (2004) Acta Crystallogr D BiolCrystallogr 60:1355-1363).

Inhibitor Compounds.

Purified protein was sent to NCCU-BRITE to screen various compoundlibraries for potential inhibitors. Nine compounds were chosen forfurther analysis. The compounds (FIG. 4A) were purchased from ASINEX.Each compound was provided as a solid powder and dissolved in 100% DMSO.

In Vitro β-Glucuronidase Assays.

In vitro assays were conducted at 50 μL total volume in 96-well, clearbottom assay plates (Costar). Substrates consisted of PNPG or PheG (FIG.9) and were acquired from Sigma. The presence of the hydrolysis productof each, PNP or Phe, was measured by absorbance at 410 nm or 540 nm,respectively. Reactions were allowed to proceed for 6 hours at 37° C.and were quenched with 100 μL of 0.2 M sodium carbonate. Absorbance wasmeasured using a PHERAstar Plus microplate reader (BMG Labtech).

Human Cell Survivability.

The nine compounds were tested for cytotoxicity in human cells. HCT116human epithelial colonic cells were grown and cultured in DMEM mediumtill confluent and adherent. Cells were counted and dilutions were madeto achieve a 50,000 cell count per reaction.

Mammalian β-Glucuronidase In Vitro Assays.

Bovine liver β-glucuronidase was acquired in lyophilized form fromSigma. The protein was dissolved and the assay was conducted aspreviously published, using PNPG as the substrate for activitydetection. (Graef et al. (1977) Clin Chem 23:532-535). Each inhibitorwas tested for an effect on mammalian β-glucuronidase activity. Reactiontime and temperature were the same as previously described (see In Vitroβ-Glucuronidase Assays).

Cell-Based Inhibition Assays.

HB101 E. coli cells were grown to an OD₆₀₀ of 0.6 in LB medium. Thesecells were then used for an in vivo assay. Reaction time and temperaturewere the same as previously described (see In Vitro β-GlucuronidaseAssays). The β-glucuronidase gene (GUS) knockout cell-line (GMS407) waspurchased from CGSC at Yale University. Absorbance was measured at theappropriate wavelength, depending on the substrate. Cell survivabilityin the presence of the nine inhibitors was tested by plating cells witheach compound.

Anaerobic In Vivo Studies.

Lactobacillus reuteri, Bifidobacterium infantis, Bacteroides vulgatusand Clostridium ramosum were provided by the Sartor Lab at theUniversity of North Carolina at Chapel Hill. Anaerobic bacteria wereplated on MRS and BHI plates. Prior to streaking, plates werepre-equilibrated in an anaerobic chamber using the BD BBL™ GasPak™ PlusAnaerobic System Envelopes.

Supplemental Methods:

Expression and Purification of E. coli β-Glucuronidase.

The full-length E. coli β-glucuronidase gene was obtained from bacterialgenomic DNA and was cloned into the pET-28a expression plasmid (Novagen)with an N-terminal 6×-Histidine tag. BL21-DE3 competent cells weretransformed with the expression plasmid and grown in the presence ofkanamycin (25 ug/ml) in LB medium with vigorous shaking at 37° C. untilan OD₆₀₀ of 0.6 was attained. The expression was induced with theaddition of 0.3 mM isopropyl-1-thio-D-galactopyranoside (IPTG) andfurther incubated at 37° C. for 4 hours. Cells were collected bycentrifugation at 4500×g for 20 min at 4° C. in a Sorvall (model RC-3B)swinging bucket centrifuge. Cell pellets were resuspended in Buffer A(20 mM Potassium Phosphate, pH 7.4, 25 mM Imidazole, 500 mM NaCl), alongwith PMSF (2 μL/mL from 100 mM stock) and 0.05 μL/mL of proteaseinhibitors containing 1 mg/mL of aprotinin and leupeptin. Resuspendedcells were sonicated and centrifuged at 14,500×g for 30 min in a Sorvall(model RC-5B) centrifuge to clarify the lysate. The cell lysate wasflowed over a pre-formed Ni-NTA His-Trap gravity column and washed withBuffer A. The Ni-bound protein was eluted with Buffer B (20 mM PotassiumPhosphate, pH 7.4, 500 mM Imidazole, 500 mM NaCl). Collected fractionswere then tested for initial purity by SDS-PAGE. Relatively pure (˜85%)fractions were combined and loaded into the Äktaxpress FPLC system(Amersham Biosciences) and passed over a HiLoad™ 16/60 Superdex™ 200 gelfiltration column. The protein was eluted into 20 mM HEPES, pH 7.4, and50 mM NaCl for crystallization and activity assays. Two milliliterfractions were collected based on highest ultraviolet absorbance at 280nm. Fractions were analyzed by SDS-PAGE (which indicated >95% purity),combined, and concentrated to 10 mg/mL for long-term storage at −80° C.

Selenomethionine Substituted β-Glucuronidase.

To express selenomethionine-substituted enzyme, B834 competent cellswere transformed with pET-28a containing the β-glucuronidase gene.SelenoMet™ Medium and Nutrient Mix (AthenaES) was prepared for growth,with 50 mg of selenomethionine added for each liter of medium. The cellswere grown at 37° C. until an OD₆₀₀ of 0.6 was reached and then wereinduced with 0.3 mM IPTG. The temperature was lowered to 15° C. and thecultures were grown overnight with shaking. Purification was performedas for the wild-type enzyme (see above).

Crystallization, Data Collection, and Phasing.

Crystals of E. coli β-glucuronidase were obtained at 2 mg/mL protein in15% PEG3350, 0.2 M Magnesium Acetate, and 0.02% Sodium Azide at 16° C.Crystals first appeared after 5 days, and grew to a final size ofapproximately 100×100×50 μm. (Pommier, 2006). Crystals werecryo-protected with perfluoropolyether vacuum pump oil (Sigma) and flashcooled in liquid nitrogen. Diffraction data were collected on the 22-BMbeam line at SER-CAT (Advanced Photon Source, Argonne NationalLaboratory). Data was indexed and scaled using HKL2000. The crystalsexhibited a space group C2, and the asymmetric unit contained twomonomers. Selenomethionine data were collected to 2.9 Å and processedsimilarly. The PHENIX software suite (AutoSol) was utilized to locateheavy atom sites and to trace a portion of the model. An initial modelwas built by hand in Coot using the SAD data and later used with Phaserfor molecular replacement with a native data set and the inhibitor boundstructure. The structure was refined using simulated annealing andtorsion angle refinement with the maximum likelihood function target inCNS, and monitored using both the crystallographic R andcross-validating R-free statistics. Data collection and refinementstatistics are presented in Table 1. The software suite PHENIX was usedfor anisotropic B-factor and TLS refinement. The model was manuallyadjusted using Coot and 2F_(o)-F_(c) and F_(o)-F_(c) electron densitymaps. The glucaro-δ-lactam model and definition files were generatedusing PRODRG, and after a ligand search using Coot, was easily placedinto electron density in the active site of both monomers.

Inhibitor Compounds.

Purified protein was sent to NCCU-BRTTE to screen various compoundlibraries for potential inhibitors. Nine compounds were chosen forfurther analysis. The compounds (FIG. 3A) were purchased from ASINEX.Each compound was provided as a solid powder and dissolved in 100%dimethyl sulfoxide (DMSO) to various concentrations.

In Vitro β-Glucuronidase Assays.

In vitro assays were conducted at 50 μL total volume in 96-well, clearbottom assay plates (Costar). Reactions consisted of the following: tenmicroliters Assay Buffer (5 μL of 5% DMSO, and 5 μl, of 500 mM HEPES, pH7.4), 30 μL substrate (various concentrations), 5 μL of an inhibitorsolution (various concentrations), and 5 μL of 5 nM enzyme. Substratesused consisted of p-nitrophenyl glucuronide (PNPG) and phenolphthaleinglucuronide (PheG) (FIG. 8) and were acquired from Sigma. The presenceof the hydrolysis product of each, p-nitrophenol (PNP) andphenolphthalein (Phe), was measured by absorbance at 410 nm or 540 nm,respectively. Reactions were allowed to proceed for 6 hours at 37° C.and were quenched with 100 μL of 0.2 M sodium carbonate. Absorbance wasmeasured using a PHERAstar Plus microplate reader (BMG Labtech). Dataacquired was analyzed using Microsoft Excel and Sigmaplot 11.0.

Human Cell Survivability.

The nine compounds were tested for cytotoxicity in human cells. HCT116human epithelial colonic cells were grown and cultured in DMEM mediumtill confluent and adherent. Cells were counted and the appropriatedilutions were made to achieve a 50,000 cell count per reaction. TheHCT116 cells were aliquoted onto a 96-well assay plate and allowed toincubate at 37° C. in media for 16 hours prior to treatment withinhibitors. After incubation, 1 μL of each inhibitor, to achieve a finalconcentration of 100 were added to the cells and further incubated for 6hours. Using the CellQuanti-Blue™ Cell Viability Assay Kit (BioAssaySystems), 10 μl, of the CellQuanti-Blue™ Reagent was added to eachreaction and incubated at 37° C. for 2 hours. After incubation with thereagent, fluorescence was measured with excitation at 544 nm andemission at 590 nm.

Mammalian β-Glucuronidase In Vitro Assays.

Bovine liver β-glucuronidase was acquired in lyophilized form fromSigma. The protein was dissolved and the assay was conducted aspreviously published, using PNPG as the primary substrate for enzymeactivity detection. The reaction mixture contained 1 μM bovine liverβ-glucuronidase and 1 mM PNPG substrate. Each of the nine inhibitorswere tested for an effect on mammalian β-glucuronidase activity byadding a concentration range of 0 to 100 μM to the reaction mixture. Thereaction was allowed to proceed for 6 hours and then quenched with 0.2 MSodium Carbonate. Absorbance was measured at the appropriate wavelength,and the data analyzed using Microsoft Excel and SigmaPlot 11.0.

Cell-Based Inhibition Assays.

HB101 E. coli cells, transformed with the pET-28a vector containing theβ-Glucuronidase gene, were grown to an OD₆₀₀ of 0.6 in LB medium. Thecells were then used in the in vivo assays to assess the glucuronidaseactivity and efficacy of the inhibitors. This assay was performed in asimilar manner to the in vitro assay: ten microliters of substrate, 1 μLof inhibitor solution, and 40 μL of cells. Again, after 6 hours ofincubation at 37° C., the reaction was quenched with 100 μL of 0.2 MSodium Carbonate. A β-glucuronidase gene (GUS) knockout cell-line(GMS407) was purchased from CGSC at Yale University. Absorbance wasmeasured at the appropriate wavelength, either 410 nm or 540 nm. Cellsurvivability in the presence of the nine inhibitors was assessed byplating a 10⁻⁵ dilution of 200 μl of saturated cells after incubationwith 100 μM of each inhibitor for 6 hours. In addition, 1 mM of eachhydrolysis product, 10 nM Tetracycline, and 2% DMSO (maximumconcentration of DMSO when 100 μM inhibitor is added) were also testedfor inhibitor effects on cell growth. Plated cells were allowed toincubate at 37° C. overnight, and colonies were counted to quantify theviability of the cells.

Anaerobic In Vivo Studies.

For the anaerobic cell lines used, two types of growth medium and agarplates were prepared: MRS medium/agar was used for Lactobacillus reuteriand Bifidobacterium infantis, and BHI medium/agar for Bacteroidesvulgatus and Clostridium ramosum. Anaerobic cell lines were graciouslyprovided by the Sartor Lab at the University of North Carolina at ChapelHill. MRS agar plates were prepared by combining MRS and agar powder, aswell as 0.1 g L-cysteine. BHI plates were produced in a similar mannerwith the addition of 0.2 mL each of 5 mg/mL heroin and 0.1% resazurin.Prior to streaking, plates were pre-equilibrated in an oxygen-freeenvironment created in an anaerobic chamber and using the BD BBL™GasPak™ Plus Anaerobic System Envelopes. One day before an assay wasconducted, 5 mL overnight cultures, using the appropriate medium, weregrown with no antibiotic present. Assay plates were prepared similar tothe E. coli cell studies, and the reaction was allowed to progress inthe anaerobic chamber for 6 hours. Absorbance data was collected afterthe reaction was quenched and analyzed.

All publications and patent applications mentioned in the specificationam indicative of the level of those skilled in the art to which thisinvention pertains. All publications and patent applications are hereinincorporated by reference to the same extent as if each individualpublication or patent application was specifically and individuallyindicated to be incorporated by reference.

Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity ofunderstanding, it will be obvious that certain changes and modificationsmay be practiced within the scope of the appended claims.

The invention claimed is:
 1. A method for attenuating side effects in asubject being administered a camptothecin-derived antineoplastic agent,the method comprising administering prior to, concurrently with or afteradministration of a camptothecin-derived antineoplastic agent atherapeutically effective amount of at least one selective entericbacterial β-glucuronidase inhibitor, wherein said side effects aresymptoms of gastrointestinal distress.
 2. The method of claim 1, whereinsaid camptothecin-derived antineoplastic agent inhibits topoisomerase I.3. The method of claim 1, wherein said camptothecin-derivedantineoplastic agent is selected from the group consisting ofcamptothecin, diflomotecan, exatecan, gimatecan, irinotecan,karenitecin, lurtotecan, rubitecan, silatecan and topotecan.
 4. Themethod of claim 3, wherein said camptothecin-derived antineoplasticagent is camptothecin or irinotecan.
 5. The method of claim 1, whereinsaid selective enteric bacterial β-glucuronidase inhibitor isadministered prior to said administration of a camptothecin-derivedantineoplastic agent.
 6. The method of claim 1, wherein said selectiveenteric bacterial β-glucuronidase inhibitor is administered concurrentlywith said administration of a camptothecin-derived antineoplastic agent.7. The method of claim 1, wherein said selective enteric bacterialβ-glucuronidase inhibitor is administered after said administration of acamptothecin-derived antineoplastic agent.
 8. The method of claim 1,wherein said selective enteric bacterial β-glucuronidase inhibitor isadministered within about two weeks of said administration of acamptothecin-derived antineoplastic agent.
 9. The method of claim 8,wherein said selective enteric bacterial β-glucuronidase inhibitor isadministered within about 1 day of said administration of acamptothecin-derived antineoplastic agent.
 10. The method of claim 9,wherein said selective enteric bacterial β-glucuronidase inhibitor isadministered within about 12 hours of said administration of acamptothecin-derived antineoplastic agent.
 11. The method of claim 1,wherein at said effective amount said selective enteric bacterialβ-glucuronidase inhibitor does not inhibit mammalian β-glucuronidases,wherein said attenuated side effect is gastrointestinal distress of saidsubject.
 12. The method of claim 1, wherein said at least one selectiveenteric bacterial β-glucuronidase inhibitor is administered to thesubject at a concentration from about 1 nM to about 1 mM.
 13. The methodof claim 1, wherein said enteric bacteria are selected from the groupconsisting of a Bacteroides sp., Bifidobacterium sp., Catenabacteriumsp., Clostridium sp., Corynebacterium sp., Enterococcus faecalis,Enterobacteriaceae, Lactobacillus sp., Peptostreptococcus sp.,Propionibacterium sp., Proteus sp., Mycobacterium sp., Pseudomonas sp.,Staphylococcus sp. and Streptococcus sp.
 14. The method of claim 1,wherein said selective enteric bacterial β-glucuronidase inhibitorexhibits selectivity for bacterial β-glucuronidases over mammalianβ-glucuronidases and the IC₅₀ mammalian-IC₅₀ bacterial ratio is greaterthan
 1. 15. The method of claim 14, wherein said IC₅₀ mammalian-IC₅₀bacterial ratio is up to about 1×10⁵.
 16. The method of claim 14,wherein said IC₅₀ mammalian-IC₅₀ bacterial ratio is at least 1×10⁵.